OVERVIEW-SUMMARY The emergence of the Severe Acute Respiratory Syndrome (SARS) in 2002-3 and the Middle East Respiratory Syndrome (MERS) in 2012 demonstrates that zoonotic coronaviruses (CoV) have and will likely continue to spread from zoonotic sources to infect human populations. MERS-CoV continues to circulate in camels and to spread to susceptible humans, highlighting the need to better understand the pathogenesis of diseases mediated by pathogenic human respiratory CoV. In this PPG, investigators with experience in coronavirus pathogenesis, molecular biology, immunology and vaccinology will work together to understand how virus factors and dysregulated innate and adaptive immune responses contribute to MERS and SARS disease in young and aged animals and in animals with co-morbidities. All of the projects will utilize newly developed mice expressing human MERS receptor (DPP4) in lieu of the mouse receptor (hDPP4-KI) and a mouse-virulent MERS-CoV, selected in these mice (MERSMA). Project 1 will use MERSMA to investigate the role of aging in infected mice. Project 1 is also based on published data showing that specific eiconsanoids with anti-inflammatory properites and their upstream phopholipases increase during aging, contributing to a delayed immune response after SARS-CoV (and by extension, perhaps MERSMA) infection. Project 2 is based on preliminary data showing that MERS-CoV has a greater dependence on host cell proteases for virus entry than does SARS-CoV. This project will investigate unique mutations found in the surface (S) glycoprotein of MERSMA that appear to affect protease function. Project 3 will investigate how MERSMA causes more severe disease than the initial human EMC/2012 strain, with focus on the ORF4b accessory protein. This project will also investigate how hDPP4 contributes to disease severity. Project 4 is based on published data showing that the CoV E protein has ion channel activity, is a virulence factor and contains a PDZ binding domain (PBM), which is critical for virus viability. This project will focus on how the E protein causes edema in lungs and on the role of the PBM in pathogenesis. A novel PBM in the C terminal of E arose in MERSMA during mouse passage and its role will be studied. This project will also continue to develop safe, live attenuated MERS and SARS vaccines. All of the projects will use the Animal/Virology Core, which will provide nonrecombinant and recombinant MERS-CoV and SARS-CoVs and will monitor and analyze infected mice. Using the Core for these purposes will maximize experimental quality control and effective use of our resources. These projects are all interrelated and collaborative, will take advantage of the unique skills and expertise of the project directors and provide new information about MERS and SARS pathogenesis that is essential to vaccine development.